1. Field of the Invention
The invention relates to an electrical switch.
2. Discussion of the Related Art
In electrical equipment used in aggressive operating conditions, precautions have to be taken to protect the electrical switch against harmful influences which impair its functional capability. Such harmful influences may be, for example, moisture, dust or the like.
Such switches have a housing in which the contact system is located, and an actuating member which is arranged in an opening on the housing, partly protrudes out of the housing and is provided for acting on the contact system with a switching effect. For protecting the switch against harmful influences, arranged on the switch is a cap of elastic material, which covers the part of the actuating member protruding out of the housing as well as the opening in the housing. On account of its elasticity, the cap allows the movement of the actuating member for switching the contact system.
A disadvantage of the known cap for protecting the switch against contaminants is that, when the switch is actuated, a relative movement takes place between the cap and the actuating member. As a result, destruction of the cap may occur after a certain period of use, in particular the friction between the cap and the actuating member may lead to cracks in the cap, so that the cap can no longer perform its protective function. Furthermore, it is disadvantageous that, on account of the elasticity of the cap, it is only possible with difficulty to ascertain visually which switching state the actuating member assumes.
DE 196 46 474 A1 further discloses an electrical switch with a cap which has a cover of a hard material and a sleeve-like part of a flexible material, designed in the manner of a bellows. The cover of the cap is of a pot-shaped design on the side facing away from the user and is arranged on the part of the actuating member protruding out of the opening in such a way that the sleeve-like part is covered by the cover. The actuating member can be moved via the side of the cover facing the user, for switching the contact system. This design of the cap requires that the switch is of a large overall form. Moreover, there is the risk of contaminants accumulating in the pot-shaped part of the cover and penetrating into the housing of the switch.
The invention is based on the object of further developing the electrical switch in such a way that the protection against ingress of contaminants into the switch is improved. Furthermore, a small switch of this type is to be provided.
A rigid plastic is expediently chosen as the material for the planar surface of the cover and a flexible plastic, such as a thermoplastic elastomer, is expediently chosen for the sleeve-like part. It is then appropriate to mold one end of the sleeve-like part on the planar surface of the cover for fastening in the manner of a two-component part. As a result, the risk of contaminants penetrating between the cover and the sleeve-like part at the particularly stressed fastening location is very low.
The planar surface of the cover may be fastened on the actuating member on the side facing away from the user by means of catch and/or snap elements. As a result, simple mounting is made possible merely by fitting the cap on, with the advantage that impairment of the protective function of the cap is not to be feared. The other end of the sleeve-like part, facing the housing, may be designed such that it can be slipped over a flange face of the housing in a simple manner or else be fitted on by means of a frame-like base.
For additionally improving the sealing of the mounting opening of an item of equipment in which the switch is fitted, a sealing lip may be arranged at the other end of the sleeve-like part or on the frame-like base. Furthermore, it is also possible to fit the switch into the mounting opening in such a way that part of the sleeve-like part on the cap at the same time seals the mounting opening into the interior of the equipment. As a result, the ingress of contaminants into the equipment is prevented in a simple manner merely by use of the switch, without additional sealing means for the equipment being necessary.
The switch according to the invention can also be designed in a simple way such that it can be illuminated, though the protection against ingress of contaminants is completely retained. For this purpose, it is sufficient to produce the planar surface of the cover from a plastic which is at least partly transparent to light in the visible spectral range. The lighting means may be arranged in a chamber of the actuating member, the chamber being covered by the planar surface of the cover. To increase the light yield in the case of a switch which can be illuminated in such a way, it is then also appropriate to produce the sleeve-like part from a plastic which is essentially opaque to light in the visible spectral range.
The advantages achieved by the invention consist in particular in that improved protection against ingress of contaminants into the interior of the housing of the switch, which may lead to impairments of the contact system located in the housing, is achieved. The risk of the cap being damaged during the period of use of the switch is greatly reduced by the hard planar surface of the cover of the cap, serving as an actuating surface. In addition, simultaneous protection of the electrical equipment, in the wall of which the switch can be fitted in a mounting opening, against ingress of contaminants through the mounting opening can also be achieved. Furthermore, the improvement in the protection for the switch also has the effect of considerably improving its service life.
In comparison with the previously used elastic caps, in which the respective switching position of the actuating member can be visually ascertained only with great difficulty, in the case of the switch according to the invention the switching position assumed by the actuating member can be easily seen. In the case of an illuminated switch, the light of the illumination is attenuated to a lesser extent than is the case with the previous elastic caps.
On account of the hard planar surface of the cover of the cap, serving as the actuating surface, the switch according to the invention can be actuated better by the user. The actuating feeling corresponds to that of a switch with which the user acts directly on the actuating member, whereby the undefinable actuating feeling in the case of a switch with the conventional elastic cap does not occur. Furthermore, an attenuation of the switching noises produced when actuating the actuating member is brought about, so that the ergonomics for the user are improved in the case of the switch according to the invention.
In spite of the sealing against contaminants, the switch according to the invention can be of a smaller design than a previous protected switch. Finally, the user can easily see that the switch is protected against ingress of contaminants, even if the switch is fitted into the wall of an electrical item of equipment. Nevertheless, the esthetics for the switch are improved in comparison with the conventional protective caps.